/Engine/Source/Runtime/Slate/Public/Framework/Docking/TabManager.h
Much like InsertNewDocumentTab, but the UnmanagedTab is not seen by the user as newly-created. e.g. Opening an restores multiple previously opened documents; these are not seen as new tabs.
void RestoreDocumentTab ( [FName](API\Runtime\Core\UObject\FName) PlaceholderId, [ESearchPreference::Type](API\Runtime\Slate\Framework\Docking\FTabManager\ESearchPreference\Type) SearchPreference, const [TSharedRef](API\Runtime\Core\Templates\TSharedRef)< [SDockTab](API\Runtime\Slate\Widgets\Docking\SDockTab) > & UnmanagedTab )